Magnetic coil



Oct. 30 1923.

H. N BOWMAN MAGNETIC COIL Filed Feb. 24, 1921 Patented out 30, 1923.

uNrrEo "STATES PATENT- orrlca.

HERMA N. BOWMAN, or NEW YORK, N. Y., ASSIGNOR 'ro WESTERN ELECTRIC oom- PANY, INCORPORATED, or NEW YQRK, Y., A-COBPORATION on NE Yonx.

'MAeNn'ric 0011..

Application filed February 24,1921. Serial No. 447 ,499.

for use in electrical systems, and particularly to coils commonly known as reactance coils.

The inductance of a reactance coil which is to be used in a particular circuitmay be varied to suit the special conditions called for in said circuit by changing the number of windings thereon. Thus, when such a coil is manufactured in accordance with certain requirements, the operator, applying the winding to the magnetic coil, tests" the inductance of the coil and if it does not comply with the desired values, the winding is either decreased or increasedas the case may be.

It is one ob ect of the present invention to provide a method of making a final adjustment of the inductance of such a coil without the necessity of adding or removing turns.

Other objects of the invention will be apparent from the description given below.

In the drawing, a magnetic core 1, consisting of two parts, is shown, said parts being 'oined together by dowels 2' and 3. Slidabiy mounted on the core 1 are two spools 4 and 5, which carry the windings of the coil.

According to this invention, the ends of' semicircular sections of the core are joined together so as to leave a slight air gap between their surfaces. It is preferable to join them by means of nonmagneticdowels which at onceincrease the air gap and hold the sections firmly together. It is then possible to vary the inductance with the greatest ease by varying the positions of the windings with respect to the joints of the core. As the windings are moved around the core in the direction of the flux, the flux leakage decreases and the inductance increases as the windings approach the air gap. This variation in inductance is sufficient to permit the adjustment of the coil, which has formerly been done by decreasing or increasing the length of the winding.

the core is reunited.

parts, inserting a dowel therein of suitable Thus the operator may wind a predetermined length of wire upon each of the spools and then place them upon the .core where the adjustment is made, as above described. In joining the parts of such a core, it is necessary that the core be'made as continuous as possible without the intervention of an excessive amount of non-magnetic material. The parts of the core may be made separately in such a manner that when joined, the opposing surfaces will touch at all points, thus reducing to a minimum the air gap between them. 7

Another possible construction is to saw or cut the core and then insert the magnetic material to compensate for that removed when the parts of the core are reunited.

Still another construction, in fact the one which appears to be the most desirable when it is possible to employ a magnetic material for the core which is more or less brittle, isto' break the core so constituted, i

thus presenting opposing surfaces, which will necessarily fit closel together when Suc a core may be made by finely dividin 'magnetic material into particles of pre etermined size and then pressing said particles together with or without a binder.

It has been found that the most desirable method of securing the parts of such a core together is by drilling or otherwise formin a small hole in the opposing surfacesof sai material, preferably non-magnetic, which may be coated with a. cementitious substance, and then applying the requisite pressure to insure a close union between said parts. It is seldom necessary to vary the inductance as much as 5% in adjusting the same and, as a coil constructed according to this invention allows over 5% variation, it v,

has been found. very satisfactory for the purpose.

What is claimed is:

1. The method of varying the inductance if of a magnetic coil having a core composed of a plurality of parts, and air gaps between the parts, and a plurality of windings on 106 said core, which consists in varying the position of said windings upon said core with relation to said air gaps.

2. The method of varying the inductance of a magnetic coil having a sectionalized 110 core and a plurality of windings slidably mounted upon said core, which consists in sliding said windings on said core a predetermined distance from the joint between the sections of said core.

3. The method of forming a magnetic coil having a particular inductance which consists in breaking an annular core, slidably mounting windings on the core, joining the parts of the core so as to form a small airgap therebetween, and adjusting the windings upon the core with relation to the joints between the parts of the core.

4. A magnetic coil comprising a section- II alized core, air gaps between the sections thereof, and means comprising dowels of non-magnetic material for holding said sections together, and windings slidably mounted upon said core.

5. A magnetic coil comprising a broken annular core, apair of windings slidably mounted one upon each section of the core, and means for reuniting the parts of the core, said means consisting in dowels of non-magnetic material inserted in the opposing surfaces of the parts of the core.

In witness whereof I hereunto subscribe my name this 10th'day of February, A. D.,

HERMAN N. BOWMAN. 

